The present invention relates to an assembly especially for a post-mix beverage-vending machine with a container that serves for the storage, cooling and carbonating of water, that is equipped with an inlet, an outlet and an electrically conductive interior wall. Inside the container the water is cooled and forms an ice layer around the interior of the side walls of the container by means of heat exchange from a cooling apparatus mounted near the side wall. The container also includes a control circuit assembly that contains a first measuring electrode, between which, and the inner wall of the container, an ohmic resistance forms that is variable in the stored medium depending on the thickness of the ice layer, and which switches the cooling apparatus on or off depending on the variable resistance.
Beverage-vending machines with a container for the storage, cooling and carbonating of drinking water are already known in which the drinking water is cooled the freezing point by means of a cooling apparatus.
A control circuit is connected in series with the cooling apparatus, with two measuring electrodes arranged inside the container to monitor the formation of the ice layer. The values obtained by the measurement electrodes are compared to a given reference value and the cooling apparatus is switched on or off depending on the comparison between the values.
A circuit assembly is known from U.S. Pat. No. 4,655,050 that controls the cooling circuit for at least two cooling regions. Here three sensors are arranged in at least one cooling range for at least two cooling demand criteria and at least one additional cooling range for at least one additional cooling demand criterion. Two sensors are arranged in a container filled with water in the region of the ice layer under formation at varying distances from the cooling apparatus.
Again in this known circuit assembly the values obtained by the sensors are each compared with a given set reference value and the cooling apparatus is switched on or off depending on comparison of the variable measured value to the corresponding set reference value.
Control of the cooling apparatus and the resulting change in the thickness of the ice layer are therefore, however, dependent on the physical-chemical composition of the water which corresponds to a certain specific ohmic resistance. The physical-chemical composition of the water and its appropriate specific resistance value can indeed differ considerably depending on local conditions and possible pre-treatment of the water. Values obtained for the specific ohmic resistance cover the range from 210.OMEGA./cm to 11 K.OMEGA./cm.
Based on this variable property of water, the switchover points for the cooling apparatus in conventional assemblies can differ greatly depending on the water utilized, and on the given reference value. Consequently, the cooling apparatus produces amounts of ice that deviate from a planned target value.